Extensive stage small cell lung cancer exists when the lung cancer is found in parts of your body outside of the lung. Standard treatment for this type of lung cancer includes chemotherapy and radiation. The chemotherapy typically consists of carboplatin and etoposide. Despite all the treatments being used, many patients get worse with this type of lung cancer. The purpose of this research study is to evaluate a new chemotherapy regimen. This chemotherapy regimen combines carboplatin and etoposide, commonly used to treat small cell lung cancer in patients with topotecan. Topotecan is a new chemotherapy agent that alone can treat patients with small cell lung cancer that has not responded to standard chemotherapy. The purpose of this study is to determine the amount of topotecan that can be used with the current standard of therapy for SCLC which is carboplatin and etoposide.